The invention relates to a device for variably adjusting the control times of gas-exchange valves of an internal combustion engine with an external rotor and an internal rotor that is arranged such that it can rotate in relation to the external rotor, wherein one of the components is drivingly connected to the crankshaft and the other component is drivingly connected to a camshaft, wherein at least one pressure space is provided and each pressure space is divided into two pressure chambers working against each other, wherein one of the pressure chambers of each pressure space acts as an advancing chamber and the other pressure chamber acts as a retarding chamber, wherein by supplying pressure medium to the advancing chambers, while simultaneously withdrawing pressure medium from the retarding chambers, the rotor interacting with the camshaft is rotated relative to the rotor interacting with the crankshaft in the direction of a maximum advanced position, wherein by supplying pressure medium to the retarding chambers, while simultaneously withdrawing pressure medium from the advancing chambers, the rotor interacting with the camshaft is rotated relative to the rotor interacting with the crankshaft in the direction of a maximum retarded position, wherein at least one first pressure medium channel and one second pressure medium channel are provided by which pressure medium can be supplied to the pressure chambers or withdrawn from these chambers, wherein at least two rotational angle limiting devices are provided and wherein each rotational angle limiting device can assume an unlocked state and a locked state, wherein the locking state can be adjusted by supplying pressure medium to or withdrawing pressure medium from the respective rotational angle limiting devices.
In modern internal combustion engines, devices for variably adjusting the control times of gas-exchange valves are used in order to vary the phase relationship between the crankshaft and the camshaft in a defined angular region between a maximum advanced position and a maximum retarded position. For this purpose, the device is integrated into a drive train by means of which torque is transferred from the crankshaft to the camshaft. This drive train can be realized, for example, as a belt, chain, or gear train.
The device comprises at least two rotors that can rotate opposite each other, wherein one rotor is drivingly connected to the crankshaft and the other rotor is locked in rotation with the camshaft. The device comprises at least one pressure space that is divided by a movable element into two pressure chambers acting against each other. The movable element is in active connection with at least one of the rotors. By supplying pressure medium to the pressure chambers or by withdrawing pressure medium from the chambers, the movable element is shifted within the pressure space, by which a selective rotation of the rotors relative to each other and thus the camshaft to the crankshaft is realized.
The supply of pressure medium to the pressure chambers or the withdrawal of pressure medium from the pressure chambers is controlled by a control unit, usually a hydraulic directional valve (control valve). The control unit is controlled, in turn, by a controller that determines and compares the actual and desired positions of the camshaft in the internal combustion engine. If there is a difference between the two positions, a signal is transmitted to the control unit that adapts the pressure medium flows to the pressure chambers to this signal.
In order to guarantee the function of the device, the pressure in the pressure medium circuit of the internal combustion engine must exceed a certain value. Because the pressure medium is usually provided by the oil pump of the internal combustion engine and the provided pressure thus increases in sync with the rpm's of the internal combustion engine, below a certain rotational number, the oil pressure is still too low to change or maintain the phase position of the rotors. This can be the case, for example, during the startup phase of the internal combustion engine or during idling phases.
During these phases, the device would execute uncontrolled oscillations, which leads to increased noise emissions, increased wear, non-smooth running, and increased raw emissions of the internal combustion engine. In order to be able to prevent this, mechanical locking devices are provided that couple the two rotors with each other locked in rotation during the critical operating phases of the internal combustion engine, wherein this coupling can be cancelled by applying pressure medium to the locking device. In this way, for the locking position it has proven advantageous to select a phase position of the camshaft relative to the crankshaft that lies between the maximum advanced position and the maximum retarded position.
Such a device is known, for example, from US 2003/0121486 A1. In this embodiment, the device has a rotary piston construction, wherein an external rotor is supported such that it can rotate on an internal rotor constructed as an impeller wheel. In addition, two rotational angle limiting devices are provided, wherein a first rotational angle limiting device allows, in the locked state, an adjustment of the internal rotor relative to the external rotor in an interval between a maximum retarded position and a defined middle position (locking position). The second rotational angle limiting device allows, in the locked state, a rotation of the internal rotor relative to the external rotor in an interval between the middle position and the maximum advanced position. If both rotational angle limiting devices are in the locked state, then the phase position of the internal rotor relative to the external rotor is limited to the middle position.
Each of the rotational angle limiting devices is made from a spring-loaded locking pin that is arranged in a receptacle of the external rotor. Each locking pin is loaded with a force by a spring in the direction of the internal rotor. On the internal rotor, a locking groove is formed that is located opposite the locking pins in certain operating positions of the devices. In these operating positions, the pins can engage in the locking groove. In this way, each rotational angle limiting device transitions from the unlocked state into the locked state.
Each of the rotational angle limiting devices can transition from the locked state into the unlocked state by applying pressure medium to the locking groove. In this case, the pressure medium forces the locking pins back into their receptacles, whereby the mechanical coupling of the internal rotor to the external rotor is cancelled.
Applying pressure medium to the pressure chambers and the locking groove is realized by the use of a control valve, wherein on the control valve there are, among other things, two work ports that communicate with the pressure chambers and one control port that communicates with the locking groove. The fact that both rotational angle limiting devices are changed from the locked state into the unlocked state by one and the same control line is a disadvantage in the shown embodiment. In this embodiment, during an adjustment process, both rotational angle limiting devices must be unlocked, that is, loaded with pressure medium, while pressure medium is alternately supplied to the pressure chambers and withdrawn from these pressure chambers. This leads to complicated control logic of the control valve. First, a plurality of control positions are required, wherein the switch points between the control positions must be constantly redefined during the operation of the internal combustion engine due to operating-dependent variations, for example, as a result of temperature changes. In addition, the setting of the individual control states requires a higher precision of the regulator system, because the flow supplied to the valve has to lie within tightly bounded flow value intervals due to the plurality of control positions. This produces a plurality of computational and data-processing operations, whereby high requirements are placed on the control electronics. In addition, the phase accuracy of the device suffers, because even small deviations in the control loop have the effect that an undesired control state is set.
In addition, in this embodiment it is provided, during the startup phase of the internal combustion engine, to connect all of the pressure chambers and the locking groove to a reservoir, which leads to an inadequate supply of lubricant to the device and thus to increased wear.
Alternatively, pressure medium provided in another embodiment is to be supplied to one of the chambers and thus a sufficient lubricant supply is to be guaranteed. However, in this embodiment the internal rotor is clamped hydraulically opposite the external rotor. This can lead to jamming of the locking pins at the edges of the locking groove, due to which hydraulic unlocking is made more difficult or optionally even prevented.